A rice (Oryza sativa L.) plant with white midrib (Oswm2) was selected from the T-DNA inserted mutant pool of rice. The basal midrib of the leaves in the mutant, except for the flag leaves, is white. The blade close to the white midrib is etiolated, and alterations of the agronomic traits, such as plant height, panicle length occur in the mutant. Genetic analysis indicated that this mutant trait was controlled by a recessive nuclear gene. To map the OsWM2 gene, an F2 population was constructed by crossing mutant Oswm2 with 02428. The OsWM2 locus was preliminarily located between the SSR molecular markers RM21478 and RM418 on chromosome 7 with the distances of 8.7 and 15.9 cM, respectively.